The objective of this study will be to investigate whether dexamethasone (DEX), a synthetic glucocorticoid useful in chemical reproductive therapy in humans, can adversely affect two functions: namely, (1) cellular aspects of the uterine metabolism during decidualized pseudopregnancy (DCPG), thereby constituting a basis for the interruption of pseudopregnancy, and (2) the body temperature rhythm during this reproductive state. Biochemical endpoints (uterine weight, protein, glycogen, progesterone, cytosolic and nuclear progesterone receptors, and plasma progesterone) during deciduoma formation on Day 10 DCPG will be investigated to help clarify the possible mechanism of DEX action. The body temperature on Days 10-12 DCPG will be studied in order to evaluate the influence of DEX on this general function. The albino rat will be employed as the mammalian model. Rats, between 200-250 grams, will be maintained under controlled photoperiodic conditions of 12L:12D (lights on at 0500 hr., off at (700 hr.) and of ambient temperature (21 degrees +/- 2 degrees C). Those rates displaying at least two consistent 4 or 5 days estrous cycle (determined by vaginal lavages) will be used. After cervical stimulation with a vibrating plastic rod during proestrus and estrus, rats will undergo the induction of uterine deciduoma on the 4th day of continuous leucocytic infiltration in the vaginal lavages. This procedure will be surgically performed via laparotomy and by scratching the inner anti-mesometrial uterine membrane with a specially designed DeFeo needle. During the post-operative recovery period, rats, divided into three groups, will be subcutaneously injected with DEX (0.5,1.0 and 1.5 mg/rat) in daily doses for 5 days (Days 5-9 DCPG). Injections will occur at 0700 hr. (2 hours after the dark phase, and biochemical tests performed during the mid-light phase at 1100 hr. on Day 10 DCPG), and at 1500 hr. (2 hours before the dark phase, and biochemical tests conducted during the mid-dark phase at 2300 hr. on Day 10 DCPG). The body temperature will be continuously monitored and analyzed by means of a computerized biotelemetry system (Dataquest III) during Days 9-10 DCPG. Each group will consist of 10 animals. Results presented as means +/- standard errors, will be tested statistically, with a p value of a least 0.05 considered significant. Dose-response, Student's t, Analysis of Variance and the Cosinor regression methods will be employed for analyses of the data.